With the development of digital world, multimedia with better and better visual effects has been highly advanced. Research and development in image and video technologies are also valued by many industrial corporations in order to enrich the color effects.
Referring to FIG. 1, conventional means for displaying image is illustrated. As shown, an image frame generally includes several image zones such as image zone A, image zone B, image zone C and image zone D. Each image zone consists of a plurality of pixels. For revealing colors of the image frame, an index value I is imparted to each pixel in the image frame so that the color values of the image frame can be realized by corresponding to each of the index values to one of the color value set in a palette array P. Accordingly, the color values of all the pixels reveal the color effect of the image frame. Each color value set includes a red color value R, a green color value G and a blue color value B, which are differentially mixed to show different colors indicated by different index values. For example, when a display exhibits a 16-color display mode, it means 16 kinds of index values are provided. Meanwhile, each index should be expressed by at least 4 bits in order to indicate 16 colors.
Give the image zone C as an example. Assume the index value of the pixels in the image zone C is 15. Then, a color value set (x, y, z) in the palette array P is pointed by the index value 15. Accordingly, the red, green and blue colors are adequately mixed to show the desired color.
Generally, patterns and colors of image frames are previously defined and stored. When there is any pattern or color change involved between frames, patterns and colors of both of the frames need to be stored in the memory pixel by pixel. In other words, the index values of all the pixels of the image frame need to be stored to show the color change. For example, when a color of a pixel changes from yellow to red, both the index value pointing to the yellow color and the index value pointing to the red color are stored in the memory so that the yellow and red color values can be displayed according to the stored index values in order to show the color change from yellow to red.
Thus, a large quantity of index values associated with sequentially changing frames need to be stored, and the quantity of data to be stored further increases with the image or video color effects. Therefore, a large capacity of memory is disadvantageously required. For example, for displaying a 640×480 image frame in a 16-color display mode, 640×480 index values need be stored, and thus the total bit number for storing one image frame will be as high as 640×480×4, i.e. 1,228,800 bits. Accordingly, once color change of the image frame occurs, double the amount 1,228,800 bits will need to be stored. It is apparent that a large storage space is required and then the cost would be high, especially in cost-oriented industries including DVD production.